MIDI keyboard controllers are a flexible tool for keyboardists. They allow a keyboardist to use their existing knowledge of keyboard layout to play a multitude of different instrument sounds. However, not all instruments are sufficiently expressively controlled by a keyboard. A MIDI keyboard can come close to simulating the expressivity and feel of an acoustic piano, but it is difficult for a keyboardist using a MIDI keyboard to reproduce the nuances of a strummed guitar or percussion instrument.
There have been musical controllers that allow for virtual strumming and control of virtual percussion instruments, but none sufficiently capture the full nuance and rhythmic expressiveness of a real acoustic instruments while utilizing a keyboardists existing knowledge of the keyboard.
What is still very much needed is a musical controller that has the expressive potential to capture the nuances of a guitar or acoustic drum.